Solid image-pickup device and method for manufacturing the solid image pickup device

ABSTRACT

It is an object of the invention to provide an improved solid image-pickup device which is compact in size and low in production cost. The solid image-pickup device is so formed that its semiconductor substrate has on its surface an image-pickup area having a plurality of light sensors arranged thereon. A transparent plate having the same shape and the same size as those of the semiconductor substrate when viewed as a plan view is bonded to the surface of the semiconductor substrate. A plurality of bonding pads are formed on the surface of the semiconductor substrate and arranged around the image-pickup area. Further, a plurality of through holes are formed through the semiconductor substrate, extending from the lower surfaces of the bonding pads to the back surface of the semiconductor substrate. An insulating film is tightly attached to the inner surface of each of the through holes, while another insulating film is tightly attached to the back surface of the semiconductor substrate. Further, each of the through holes is filled with an electrically conductive material, thereby effecting an electric connection between the bonding pads and the copper wire of the flexible circuit substrate bonded to the back surface of the semiconductor substrate.

This application claims priority to Japanese Patent Application NumberJP2001-308512 filed Oct. 4, 2001 which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a solid image-pickup device and amethod for manufacturing the solid image-pickup device. In particular,this invention relates to a technique for manufacturing an improvedsolid image-pickup device which is compact in size and low in productioncost.

2. Description of the Related Art

FIG. 6 is a cross sectional side view showing a conventional solidimage-pickup device.

As shown in FIG. 6, the conventional solid image-pickup device 102includes a package 104 having an internal recess portion 106. A solidimage-pickup element 108 formed by disposing light sensors and the likeon a semiconductor substrate is received into the internal recessportion 106, with its light receiving surface facing upward. Along theedge portions of the surface of the solid image-pickup element, thereare arranged a plurality of bonding pads 112. These bonding pads 112 areconnected through bonding wires 116 with terminal electrodes 114 of thepackage 104. Each of the terminal electrodes 114 is connected with oneend of one of external terminals 118 inserted through the package 104,while the other end of such one external terminal 118 is allowed toproduce to the outside of the package 104 from the backside thereof.

Above the solid image-pickup element 108 there is disposed a transparentplate 120 which is provided to protect the solid image-pickup element108 in order to ensure its reliability. Specifically, the transparentplate 120 is adhesively fixed on the package 104 above the recessportion 106, so as to ensure an airtight state within the recess portion106 of the package 104.

However, with regard to the above-described conventional solidimage-pickup device, since the solid image-pickup element 108(semiconductor substrate) has to be received into each package 104, anentire size of the solid image-pickup device has to be larger than thesolid image-pickup element 108. Moreover, since the external terminals118 are protruding from the backside of the package 104, it isimpossible to avoid an increase in the thickness of the package 104containing the external terminals 118.

Moreover, with regard to the above-described conventional arrangement,since the solid image-pickup element 108 has to be received into thepackage 104 in order to complete a packaging process, it is necessary toperform an operation in which the bonding pads 112 of the solidimage-pickup elements 108 have to be connected with the terminalelectrodes 114 of the package 104 by way of the bonding wires 116. As aresult, it is difficult to ensure a high production efficiency as wellas a low production cost.

On the other hand, it is extremely important for a digital still camera,a video camera or a PDA (Personal Digital Assistants) apparatus to bemade compact in size and low in cost. For this reason, the solidimage-pickup device 102 which serves as a main component to beincorporated into each of these apparatus, is usually strongly requiredto be made compact in size and low in production cost.

SUMMARY OF THE INVENTION

The present invention has been accomplished in order to solve theaforementioned problem, and it is an object of the invention to providean improved solid image-pickup device which is compact in size and lowin production cost, as well as to provide a method for manufacturingsuch an improved solid image-pickup device.

In order to achieve the above object of the present invention, there isprovided an improved solid image-pickup device including a semiconductorsubstrate having a plurality of light sensors and a plurality of bondingpads on the surface, a transparent plate fixed on the surface of thesemiconductor substrate, the surface of the transparent plate surfacefacing the light sensors; through holes extending from the lowersurfaces of the bonding pads to the back surface of the semiconductorsubstrate; a first insulating film covering the inner surfaces of thethrough holes; a second insulating film surrounding at least theopenings of the through holes at the back surface of the semiconductorsubstrate; and an electrically conductive material supplied in thethrough holes, electrically connected with the lower surfaces of thebonding pads, and exposed from the openings of the through holes.

Further, according to the present invention, there is also provided amethod of manufacturing solid image-pickup devices including asemiconductor substrate having a plurality of light sensors and aplurality of bonding pads on the surface, the method comprising thesteps of: bonding a transparent plate to a surface of a semiconductorwafer, the surface including a plurality of semiconductor substrateportions for a plurality of solid image-pickup devices, the transparentplate having a plate surface facing the surface of the semiconductorwafer and having substantially the same size as that of thesemiconductor wafer; grinding the back surface of the semiconductorwafer bonded with the transparent plate, to reduce the thickness of thesemiconductor wafer; forming through holes extending from the backsurface of the semiconductor wafer to the lower surfaces of the bondingpads; forming a first insulating film on the inner surface of each ofthe through holes; forming a second insulating film on the back surfaceof the semiconductor wafer so as to surround at least the openings ofthe through holes; and cutting the semiconductor wafer together with thetransparent plate to form a plurality of solid image-pickup devices.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a cross sectional side view showing a solid image-pickupdevice formed according to one embodiment of the present invention.

FIG. 1B is an enlarged cross sectional view showing portion IB of FIG.1A.

FIG. 2 is a plan view showing the solid image-pickup device formedaccording to the embodiment of the invention.

FIG. 3 is a side view showing the solid image-pickup device, when viewedfrom a position under the drawing in FIG. 2.

FIG. 4 is a side view showing the solid image-pickup device, when viewedfrom a position on the right side of the drawing in FIG. 2.

FIG. 5 is a back view of the solid image-pickup device formed accordingto the embodiment of the present invention.

FIG. 6 is a side view showing a conventional solid image-pickup device.

FIG. 7A is a cross sectional side view showing a solid image-pickupdevice formed according to another embodiment of the present invention.

FIG. 7B is an enlarged cross sectional view showing portion VIIB of FIG.7A.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention will be described in thefollowing with reference to the accompanying drawings.

FIG. 1A is a cross sectional side view showing a solid image-pickupdevice formed according to one embodiment of the present invention. FIG.1B is an enlarged cross sectional view showing portion IB of FIG. 1A.FIG. 2 is a plan view showing the solid image-pickup device formedaccording to the embodiment of the invention. FIG. 3 is a side viewshowing the solid image-pickup device, when viewed from a position underthe drawing in FIG. 2. FIG. 4 is a side view showing the solidimage-pickup device, when viewed from a position on the right side ofthe drawing in FIG. 2. FIG. 5 is a back view of the solid image-pickupdevice formed according to the embodiment of the present invention.Specifically, FIG. 1A and FIG. 1B are cross sectional views taken alongIA—IA line in FIG. 2.

As shown in FIGS. 2 through 5, the solid image-pickup device 2 formedaccording to the present embodiment comprises a solid image-pickupelement 4, a transparent plate 6 and a flexible circuit substrate 8.

The solid image-pickup element 4 includes a plurality of light sensorsarranged in an image-pickup area 14 which is rectangular in shape andlocated in the central area on the surface 12 of a semiconductorsubstrate 10, also includes a plurality of bonding pads 16 along theedge portions of the surface of the semiconductor substrate. Thesemiconductor substrate 10 has a thickness of 100 μm or less, while thetransparent plate 6 may be formed by a quartz glass. Both the solidimage-pickup element 4 and the transparent plate 6 are rectangular inshape when viewed as plan views, and have the same shape as well as thesame size. The transparent plate 6 is fixed on the surface 12 of thesemiconductor substrate 10, in a manner such that the two members arecaused to face each other and be coincident in their positions.

Specifically, the ridge line portions 18 (located opposite to thesemiconductor substrate 10) of the transparent plate 6 are chamfered, asshown in FIGS. 3 and 4.

As shown in FIG. 1, the semiconductor substrate 10 and the transparentplate 6 are bonded to each other by virtue of a sealing agent 20. Here,the sealing agent 20 is applied to the edge portions of thesemiconductor substrate 10 and the transparent plate 6, extending aroundthe entire image-pickup area 14. In this way, corresponding to thecentral portions of both the semiconductor substrate 10 and thetransparent plate 6, a clearance having a thickness corresponding to thethickness of the sealing agent 20 is formed between the surface 12 ofthe semiconductor substrate 10 and the lower surface of the transparentplate 6, forming an internal space 22 which is in an airtight state byvirtue of the sealing agent.

Further, the semiconductor substrate 10 is formed with a plurality ofthrough holes 26, located in positions corresponding to the bonding pads16, and extending from the lower surfaces of the bonding pads 16 to theback surface 24 of the semiconductor substrate 10. Specifically, thediameter of each of the through holes 26 is smaller than that of each ofthe bonding pads 16, and the internal surface of each through hole 26 iscoated with an insulating film 28. Moreover, an entire area of the backsurface 24 of the semiconductor substrate 10 (not including the openingsof the through holes 26) is coated with an insulating film 30 having athickness of several microns. In practice, both the insulating film 28and the insulating film 30 may be formed by a polyimide resin.

A flexible circuit substrate 8 is bonded through an adhesive agent 32 tothe back surface 24 of the semiconductor substrate 10, in a manner suchthat the plate surface of the circuit substrate 8 can face the backsurface 24 of the semiconductor substrate 10. Further, a copper wire 34serving as an external lead wire for the solid image-pickup device 2 isprovided on the surface of the flexible circuit substrate 8. Tn thismanner, the flexible circuit substrate 8 is bonded to the semiconductorsubstrate 10, with the copper wire 34 being located on the outside ofthe device. Further, on the flexible circuit substrate 8 andcorresponding to the through holes 26, there are formed a plurality oflands 36 (see FIG. 5) in connection with the copper wire 34.Specifically, each of the lands 36 is formed with a through hole havinga diameter larger than each through hole 26, and openings havingsubstantially the same diameters are formed in the correspondingpositions through the above adhesive agent layer 32.

Then, an amount of electrically conductive material 38 which willprotrude to the lands 36 is used to fill the through holes 26 of thesemiconductor substrate 10 and the through holes of the flexible circuitsubstrate 8. In this manner, by way of such an electrically conductivematerial 38, the bonding pads 16 of the semiconductor substrate 10 aswell as the lands 36 of the flexible circuit substrate 8 can beelectrically connected with the copper wire 34. Here, in more detail,the electrically conductive material 38 may be formed by hardening anelectrically conductive paste.

In fact, the flexible circuit substrate 8 is formed such that itslongitudinal direction can be arranged in the lateral direction of theimage-pickup device, and that one end thereof is extending to one sideof the semiconductor substrate 10.

In this way, since the solid image-pickup device 2 of the presentembodiment is constructed in a manner such that the transparent plate 6is disposed to cover the surface 12 of the semiconductor substrate 10 onwhich light sensors are arranged, such an arrangement is different froma conventional image-pickup device in which the semiconductor substrateis received into a package. Namely, when viewed as a plan view, thedevice of the present embodiment has only a size which is exactly thesame as the semiconductor substrate 10. Further, the thickness of thedevice includes only the thicknesses of the transparent plate 6 and thesemiconductor substrate 10. For this reason, it is possible to greatlyreduce the size of the solid image-pickup device 2, especially thethickness thereof.

Further, since the flexible circuit substrate 8 is disposed to cover theback surface 24 of the solid image-pickup device 2, and since thebonding pads 16 on the semiconductor substrate 10 are connected with thewire on the flexible circuit substrate 8 by virtue of the electricallyconductive material 38 received in the through holes 26, it is possibleto obtain an improved thickness-reduced image-pickup device including anexternal circuit (flexible circuit substrate 8).

Usually, in an apparatus such as digital still camera containing thesolid image-pickup device 2, since an optical lens is disposed in frontof the solid image-pickup device 2, the apparatus as a whole is likelyto become thick in its thickness. For this reason, the fact that it hasbecome possible to produce a thickness-reduced solid image-pickup device2 is extremely favourable in producing an improved optical apparatuswhich is thin in its thickness.

Besides, according to the present embodiment of the invention, since theridge line portions 18 of the transparent plate 6 are chamfered, whenthe solid image-pickup device 2 is installed into an optical apparatusand when the transparent plate 6 accidentally bumps against a lens blockor the like within the optical apparatus. it is possible to prevent thetransparent plate 6 from getting broken off.

Further, when the solid image-pickup device 2 is installed into adigital still camera or the like, if (for example) reference surfaces40, 42 and 44 set on the side surface of the transparent plate 6 areused as the working reference, it is possible to incorporate the solidimage-pickup device into the camera in an accurate positioning processwith a high precision. Moreover, as shown in FIG. 3, the referencesurfaces 40 and 42 are set on the same side surface 46 of thetransparent plate, but mutually separated from each other at apredetermined interval. However, the reference surface 44, as shown inFIG. 4, is set on the other side surface 48 of the transparent plate,perpendicular to the side surface 46. In this way, even if the sidesurfaces of the transparent plate 6 are used as references, since thereare no positional dislocations between the side surfaces of thetransparent plate 6 and the side surface of the semiconductor substrate10, it is possible to carry out the positioning of the semiconductorsubstrate 10 with a high precision. Further, a precision in positionalrelation between the side surface of the semiconductor substrate 10 andthe image-pickup area 14 can be determined in accordance with a cuttingprecision when the wafer is cut and individual solid image-pickupdevices 2 are obtained. In fact, such a precision can be made at 10 μmor less. Accordingly, it is possible to carry out the positioning of theimage-pickup area 14 with respect to an optical apparatus, with only anextremely small error of 10 μm or less. Moreover, since it is possibleto easily perform the positioning with a high precision, it is allowedto shorten a working time necessary for installing the solidimage-pickup device 2 into an optical apparatus.

The solid image-pickup device 2 having the above-described structure canbe manufactured at an extremely low cost, with the use of a method whichwill be explained in detail below.

One example of a method for manufacturing the solid image-pickup device2 according to the present invention will be described with reference toFIGS. 1 through 5.

At first, a transparent plate having the same size as that of asemiconductor wafer is bonded (by means of the sealing agent 20, i.e.,an adhesive agent) to the surface of the semiconductor wafer on whichsemiconductor substrate portions for a plurality of solid image-pickupdevices have been formed. During the bonding process, the sealing agent20 is applied to either the semiconductor wafer or the transparentplate, corresponding to the respective solid image-pickup devices to beformed on the semiconductor wafer, in a manner such that eachimage-pickup area 14 is surrounded by the sealing agent, thereby bondingtogether the semiconductor wafer and transparent plate. Then, thesealing agent 20 is hardened by heating or by irradiating with anultraviolet light.

Subsequently, the back surface of the semiconductor wafer, on which thetransparent plate has been bonded, is ground so as to reduce thethickness of the semiconductor wafer to 100 μm or less.

Afterwards, the trough holes 26 are formed extending from the backsurface of the semiconductor wafer to the lower surfaces of the bondingpads 16. In forming these through holes, it is allowed to employ one ofseveral commonly used processes, such as a process using a laser, aprocess using a photolithography technique or the like.

Then, the inner surface of each through hole 26 is coated with aninsulating film 28 formed by a polyamide resin, while the back surface24 (not including the openings of the through holes 26) of thesemiconductor wafer is coated with an insulating film 30. Here, theinsulating film 30 may be a polyimide tape.

Subsequently, the semiconductor wafer along with the transparent plateare cut into several smaller portions corresponding to the respectivesolid image-pickup devices, thereby individually obtaining solidimage-pickup devices. At this time, if several grooves each having aV-shaped cross section are formed in advance on the surface of thetransparent plate before the cutting process is carried out, and if thesemiconductor wafer together with the transparent plate are cut alongthese grooves, it is possible to obtain a plurality of solidimage-pickup devices each having such a transparent plate that its ridgeline portions have been chamfered.

Afterwards, a flexible circuit substrate 8 is bonded to the back surface24 of each small semiconductor wafer, while the through holes 26 arefilled with an electrically conductive paste which is then heated so asto be hardened, thereby rendering the bonding pads 16 of thesemiconductor substrate 10 to be electrically connected with the copperwire 34 of the flexible circuit substrate 8.

With the use of the manufacturing method described above, it is notnecessary to perform a conventional operation in which semiconductorsubstrates are individually received into the respective packages toform the respective solid image-pickup devices, while the packages andthe semiconductor substrates are connected with each other through thebonding wires. Moreover, since the transparent plate can be bonded tothe semiconductor wafer and subsequent processes can be carried outdealing with only the integrally bonded body, it is possible to producea large number of solid image-pickup devices during each one operation,thereby making it possible to greatly reduce the production cost.

However, the method of the present invention for manufacturing the solidimage-pickup element and the solid image-pickup device should not belimited to the above-described example. In fact, it is also possible tocarry out one of some other methods without departing from the scopeprescribed by the spirit of the present invention.

For example, although the above description shows that each flexiblecircuit substrate 8 is bonded to the back surface 24 of eachsemiconductor substrate 10, it is also allowed not to use the flexiblecircuit substrate 8. Namely, it is effective that after the back surfaceof the semiconductor substrate 10 is subjected to an insulatingtreatment, bumps or the like are formed on the openings of the throughholes 26.

Further, although the present embodiment shown in FIG. 1 indicates thatthe sealing agent is applied to the edge portions of the semiconductorsubstrate and the transparent plate in a manner such that the appliedsealing agent extends around the entire image-pickup area, it is alsopossible to employ a method shown in FIG. 7 which indicates that alight-transmissible material may be used in the sealing agent, and sucha sealing agent may be interposed between the entire surface of thesemiconductor substrate and the transparent plate. In this way,especially in a process for manufacturing an image-pickup device whichis required to be compact in size, it is not necessary to control theforming position of the sealing agent with respect to an image-pickuparea, and in a process of bonding together the semiconductor wafer andthe transparent plate, it is allowed to apply the sealing agent to theentire surface of the semiconductor wafer. For this reason, even if itis difficult to control the forming position of the sealing agent asshown in the structure of FIG. 1, it is still possible to manufacturethe image-pickup device which is compact in size.

As described in the above, the solid image-pickup device of the presentinvention and the solid image-pickup device manufactured using themethod of the present invention, are constructed in a manner such thatthe transparent plate is disposed to cover the surface of thesemiconductor substrate on which light sensors have been arranged.Therefore, such an arrangement is different from a conventionalstructure in which a semiconductor substrate is received into acorresponding package. Namely, when viewed as a plan view, the device ofthe present invention has only a size which is exactly the same as thesemiconductor substrate. Further, the thickness of the device includesthe thicknesses of the transparent plate and the semiconductorsubstrate. For this reason, it is possible to greatly reduce the size ofa solid image-pickup device, especially the thickness thereof.

Further, since the flexible circuit substrate is disposed to cover theback surface of the solid image-pickup device, and since the bondingpads on the semiconductor substrate are connected with the wire on theflexible circuit substrate by virtue of the electrically conductivematerial received in the through holes, it is possible to obtain animproved thickness-reduced image-pickup device including an externalcircuit.

As a result, it is not necessary to perform a conventional operation inwhich semiconductor substrates are individually received into thepackages corresponding to the respective solid image-pickup devices,while the packages and the semiconductor substrates are connected witheach other through the bonding wires. Moreover, since the transparentplate can be bonded to the semiconductor wafer, and subsequent processescan be carried out with respect to the integrally bonded body, it ispossible to produce a large number of solid image-pickup devices duringeach one operation, thereby making it possible to greatly reduce theproduction cost.

1. A solid image-pickup device comprising: a semiconductor substratehaving a plurality of lights sensors and a plurality of bonding padslocated at a first side wherein each of said bonding pads is acontiguous solid structure having no internal voids extending throughboth upper and lower surfaces; through holes extending from a secondside of said semiconductor substrate to lower surfaces of the bondingpads; an insulating film covering inner surfaces of the through holes;and an electrically conductive material filled in the through holes,electrically connected with the lower surfaces of the bonding pads, andexposed from the openings of the through holes at said second side ofsaid semiconductor substrate and wherein a transparent plate is fixedover a surface of the semiconductor substrate with a sealing agentdisposed between the transparent plate and the semiconductor substrate,said sealing agent disposed exclusively along edge portions of thesurface of the semiconductor substrate and surrounding at least all thelight sensors, with an internal void surrounded by the sealing agentbeing sealed airtight.
 2. A solid image-pickup device comprising: asemiconductor substrate having a plurality of lights sensors and aplurality of bonding pads located at a first side wherein each of saidbonding pads is a contiguous solid structure having no internal voidsextending through both upper and lower surfaces; through holes extendingfrom a second side of said semiconductor substrate to lower surfaces ofthe bonding pads; an insulating film covering inner surfaces of thethrough holes; and an electrically conductive material filled in thethrough holes, electrically connected with the lower surfaces of thebonding pads, and exposed from the openings of the through holes at saidsecond side of said semiconductor substrate and further comprising aflexible circuit substrate, the face thereof being fixed adjacent tosaid second surface of the semiconductor substrate; wherein a wireprovided on the flexible circuit substrate is electrically connectedwith the electrically conductive material exposed from the openings ofthe through holes at said second side of said semiconductor substrate.3. A solid image-pickup device comprising: a semiconductor substratehaving a plurality of light sensors and a plurality o bonding padslocated at a first side of the substrate wherein each of said bondingpads is a contiguous solid structure having no internal voids extendingthrough both upper and lower surfaces; a transparent plate fixed over asurface of said semiconductor substrate, through holes extending from asecond side of said semiconductor substrate to lower surfaces of thebonding pads; a first insulating film covering inner surfaces of thethough hole; an electrically conductive material filled in the thoughholes, electrically connected with the lower surfaces of the bondingpads; and wherein the transparent plate is fixed on the semiconductorsubstrate with a sealing agent disposed between the transparent plateand the semiconductor substrate, said sealing agent disposed exclusivelyalong edge portions of the surface of the semiconductor substrate andsurrounding at least all the light sensors, with an internal voidsurrounded by the sealing agent being sealed airtight.